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M L Halperin

Publications and source records attributed to M L Halperin.

At least 253 records · Page 14Linked to original sources
PubMed1971

The inhibition by methylmalonic acid of malate transport by the dicarboxylate carrier in rat liver mitochondria. A possible explantation for hypoglycemia in methylmalonic aciduria.

We report the effects of methylmalonic acid (MMA) on the mitochondrial transport systems for malate, alpha-oxoglutarate, and isocitrate. MMA is shown to be a substrate for all three carrier systems, and an inhibitor of the malate-phosphate exchange carrier. The effects of MMA on the metabolism of malate, oxoglutarate, and isocitrate by rat liver mitochondria are demonstrated to be mediated by the influence of MMA on the transport step. A hypothesis regarding the metabolic impairments responsible for hypoglycemia and ketonemia in methylmalonic aciduria is formulated in relation to these findings.

Animals↗
PubMed1971

Reduction in adipocyte ATP by lipolytic agents: relation to intracellular free fatty acid accumulation.

Epinephrine, norepinephrine, ACTH, and dibutyryl 3',5'-cyclic AMP reduced adipocyte ATP levels during 60 min incubation; glucose displayed a protective effect. The reduction in adipocyte ATP levels could not be attributed solely to: a direct hormone effect, deficiency in metabolic substrate, activation of adenyl cyclase with ATP consumption, loss of adenine nucleotide from the cell or loss of cells during incubation, lipolytic rate per se, or extracellular accumulation of FFA or glycerol. To determine whether intracellular FFA accumulation was a causative factor, intracellular FFA levels were measured during hormone-stimulated lipolysis. This was accomplished by using sucrose-U-(14)C as a marker for the extracellular space to correct for contamination of cells by extracellular albumin-bound FFA. These experiments showed that the fall in adipocyte ATP correlated with FFA saturation of medium albumin and progressive accumulation of FFA within the adipocyte. Furthermore, the protective effect of glucose noted above was associated with a marked reduction in intracellular FFA as compared to the extracellular FFA pool. On the basis of these studies, combined with those in the literature, it is concluded that in vitro effects of lipolytic agents on adipocyte ATP levels are the net result of imparied ATP synthesis (uncoupled oxidative phosphorylation) in the face of normal or augmented ATP consumption.

Adenosine Triphosphate↗
PubMed1971

Intracellular accumulation of free fatty acids in isolated white adipose cells.

A simple, rapid, and accurate method was developed for measuring intracellular FFA levels in isolated white adipose cells using sucrose-(14)C or inulin carboxyl-(14)C as nontransportable, nonutilizable markers of the extracellular space. Following incubation, medium and cells were separated by centrifugation and the infranatant medium was removed by aspiration. The volume of medium trapped between cells was determined by measuring the amount of sucrose-(14)C or inulin carboxyl-(14)C retained in the floating packed adipose cells. In this way the FFA content of the adipose cells could be corrected for contamination by FFA bound to extracellular albumin. With this technique the initial events in hormone-activated lipolysis were studied under conditions of maximal and constant rates of triglyceride hydrolysis. The FFA content of isolated adipocytes of fed rats was 0.5 micro mole/g cell lipid. On addition of norepinephrine in the presence of medium albumin, the concentration of intracellular FFA rapidly increased and reached a plateau at a concentration of 2-2.5 micro moles/g cell lipid. In the presence of medium albumin an initial lag in glycerol release occurred and this was attributed to partial hydrolysis of triglyceride with retention of lower glycerides. After 5 min of incubation FFA and glycerol output was constant. In the absence of medium albumin norepinephrine-stimulated lipolysis was reduced more than 90% and extracellular FFA release was not detected. Nevertheless, intracellular FFA accumulation was identical to that seen in the presence of albumin. The data suggest that most of this intracellular pool of FFA is bound to cytoplasmic constituents.

Adipose Tissue↗
PubMed1970

Transport of reduced nicotinamide-adenine dinucleotide into mitochondria of rat white adipose tissue.

Mitochondria from rat white adipose tissue were prepared, exhibiting good respiratory control and P/O ratios. They would not oxidize NADH unless NNN'N'-tetramethyl-p-phenylenediamine was added as a carrier of reducing equivalents. These mitochondria were found to oxidize neither l-glycerol 3-phosphate nor l-glutamate plus l-malate at significant rates. The activity of aspartate aminotransferase in these mitochondria was found to be low compared with that found in rat liver mitochondria. As a consequence of this, the adipose-tissue mitochondria exhibited very low rates of cytoplasmic NADH oxidation in a reconstituted Borst (1962) cycle compared with liver mitochondria.

Adipose Tissue↗
PubMed1970

The role of the cytoplasmic redox potential in the control of fatty acid synthesis from glucose, pyruvate and lactate in white adipose tissue.

The metabolism of lactate, pyruvate and glucose was studied in epididymal adipose tissue of starved, normally fed and starved-re-fed rats. Lactate conversion into fatty acid occurred at an appreciable rate only in the adipocyte of starved-re-fed animals. NNN'N'-Tetramethyl-p-phenylenediamine, an agent that transports reducing power from the cytoplasm to the mitochondria, caused large increments of fatty acid synthesis from lactate and a smaller one from glucose but a decrease in that from pyruvate. Glucose (1.0mm) increased fatty acid synthesis from lactate 4.3-fold but only 1.67-fold from pyruvate in adipocytes from normally fed animals. 2-Deoxyglucose decreased fatty acid synthesis from lactate to a greater degree (threefold) compared to that from pyruvate in adipocytes from starved-re-fed animals. l-Glycerol 3-phosphate contents were approximately equal in epididymal fat-pads, incubated in the presence of lactate or pyruvate, from normally fed animals, whereas the addition of 1mm-glucose resulted in a tenfold increase in l-glycerol 3-phosphate content only in the presence of lactate. The l-glycerol 3-phosphate content was tenfold higher in adipose tissue from starved-re-fed animals incubated in the presence of lactate than in the presence of pyruvate. 2-Deoxyglucose caused these values to be slightly lowered in the presence of lactate. We suggest that lactate metabolism is limited by the rate of NADH removal from the cytoplasm. In the starved-re-fed state, this occurs by reduction of dihydroxyacetone phosphate formed from glycogen to produce l-glycerol 3-phosphate, thus permitting lactate conversion into fatty acid. When glucose is the substrate, and rates of transport are not limiting, the rate of removal of cytoplasmic NADH limits glucose conversion into fatty acid.

Adipose Tissue↗
PubMed1969

Regulation of glycolysis and L-glycerol 3-phosphate concentration in rat epididymal adipose tissue in vitro. Role of phosphofructokinase.

1. Attempts were made to define the role of phosphofructokinase in glycolytic control and the factors regulating the concentration of l-glycerol 3-phosphate in rat epididymal fat pads incubated in vitro. 2. Glycolysis rates were altered by anoxia or by additions of insulin, adrenaline or both to the incubation medium, and the changes in rate were related to changes in the steady-state concentrations of hexose phosphates, adenine nucleotides, l-glycerol 3-phosphate and citrate in the whole tissue. Measurements were also made of the lactate/pyruvate concentration ratio in the medium after incubation. 3. The mass-action ratios of phosphofructokinase, calculated from the whole-tissue concentrations of products and substrates, were less than 0.1% of the value of the ratio at pH7.4 at equilibrium. 4. Only in the presence of adrenaline could the observed stimulation of glycolytic flux be related to a possible activation of phosphofructokinase since, in this situation, the concentration of one substrate, fructose 6-phosphate, was not altered and the concentration of the other, ATP, was decreased. Increased glycolytic flux in the presence of insulin may be explained by an observed increase in the concentration of the substrate, fructose 6-phosphate. Under anaerobic conditions, glycolytic flux was decreased but this did not appear to be the result of inhibition of phosphofructokinase, since the concentrations of both substrates, fructose 6-phosphate and ATP, were decreased. The changes in glycolytic flux with insulin and anoxia may be secondary to changes in the rate of glucose uptake. 5. Changes in l-glycerol 3-phosphate concentration appear to be related both to changes in the concentration of dihydroxyacetone phosphate and to changes in the NADH/NAD(+) concentration ratio in the cytoplasm. They do not seem to be related directly to alterations in glycolytic rate.

Adenine Nucleotides↗
PubMed1968

The control of fatty acid and triglyceride synthesis in rat epididymal adipose tissue. Roles of coenzyme A derivatives, citrate and L-glycerol 3-phosphate.

1. Methods are described for the extraction and assay of acetyl-CoA and of total acid-soluble and total acid-insoluble CoA derivatives in rat epididymal adipose tissue. 2. The concentration ranges of the CoA derivatives in fat pads incubated in vitro under various conditions were: total acid-soluble CoA, 0.20-0.59mm; total acid-insoluble CoA, 0.08-0.23mm; acetyl-CoA, 0.03-0.14mm. 3. An investigation was made of some postulated mechanisms of control of fatty acid and triglyceride synthesis in rat epididymal fat pads incubated in vitro. The concentrations of intermediates of possible regulatory significance were measured at various rates of fatty acid and triglyceride synthesis produced by the addition to the incubation medium (Krebs bicarbonate buffer containing glucose) of insulin, adrenaline, albumin, palmitate or acetate. 4. The whole-tissue concentrations of glucose 6-phosphate, l-glycerol 3-phosphate, citrate, acetyl-CoA, total acid-soluble CoA and total acid-insoluble CoA were assayed after 30 or 60min. incubation. The rates of fatty acid and triglyceride synthesis, calculated from the incorporation of [U-(14)C]glucose into fatty acids and glyceride glycerol respectively, and the rates of glucose uptake, lactate plus pyruvate output and glycerol output were measured over a 60min. incubation. 5. The rate of triglyceride synthesis could not be correlated with the concentrations of either l-glycerol 3-phosphate or long-chain fatty acyl-CoA (measured as total acid-insoluble CoA). Factor(s) other than the whole-tissue concentrations of these recognized precursors appear to be involved in the determination of the rate of triglyceride synthesis. 6. No relationship was found between the rate of fatty acid synthesis and the whole-tissue concentrations of the intermediates, citrate or acetyl-CoA, or with the two proposed effectors of acetyl-CoA carboxylase, citrate (as activator) or long-chain fatty acyl-CoA (as inhibitor). The control of fatty acid synthesis appears to reside in additional or alternative factors.

Acetates↗
PubMedDate not supplied

Protein conversion to glucose: an evaluation of the quantitative aspects.

The amount of glucose that can be synthesized from a protein depends on its amino acid (AA) composition. This value is about 60 g from 100 g of liver or muscle protein and is based on a knowledge of the total AA content and the proportion of each AA that can be converted to pyruvate. The maximum quantity of glucose in grams that can be synthesized from administered AA solutions is the sum of the products of the number of moles of each AA times its percent convertible to pyruvate times the molecular weight of that AA.

Amino Acids↗
PubMedDate not supplied

The urine anion gap: the critical clue to resolve a diagnostic dilemma in a patient with ketoacidosis.

Usually, ketoacidosis presents few if any diagnostic or therapeutic problems; in this article, we report a case where ketoacidosis was clinically occult and biochemically obscure. The patient presented with acute pancreatitis associated with a modest antecedent alcohol intake. Metabolic acidosis with a normal anion gap (10 meq/L) was observed together with moderate hyperglycemia and a 2 + (but not 4 +) test for serum ketones. None of the usual causes of metabolic acidosis with a normal anion gap was identified nor was there an obvious explanation for a reduction in unmeasured anion gap (e.g., hypoalbuminemia, dysproteinemia, or the presence of abnormal halides). Despite the initial normal anion gap, ketoacidosis was suspected clinically and this was confirmed by the elevated serum B-hydroxybutyrate of 8 mmol/L. We deduced that the serum unmeasured anions, which should have been increased by at least 8 meq/L, were being underestimated because of the effect of hypertriglyceridemia on the serum chloride determination. When the serum chloride was reestimated by a method not influenced by hyperlipidemia, the value was 102 mmol/L not 112 mmol/L and, when reevaluated, the anion gap was indeed appropriately elevated. In addition, the urine anion gap (Na + K - Cl) was 103 meq/L in the absence of renal disease. This indicated that the expected large quantity of urinary ammonium must have been masked by an even greater quantity of unmeasured anion; in this case proven by direct measurement to be B-hydroxybutyrate. Finally, metabolism of the alcohol ingested, which yields hepatic NADH, could explain, in part, the modest hyperglycemia and the absence of a 4 + test for serum ketones.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗